diff --git a/desktop_env/evaluators/metrics/utils.py b/desktop_env/evaluators/metrics/utils.py
index 6f444f8..7036080 100644
--- a/desktop_env/evaluators/metrics/utils.py
+++ b/desktop_env/evaluators/metrics/utils.py
@@ -124,10 +124,14 @@ def load_charts(xlsx_file: Workbook, sheet_name: str, **options) -> Dict[str, An
                 value_str: str = ser.val.numRef.f
             elif hasattr(ser.val, "strRef") and hasattr(ser.val.strRef, "f"):
                 value_str: str = ser.val.strRef.f
+            else:
+                value_str: str = ""
             if hasattr(ser.cat, "numRef") and hasattr(ser.cat.numRef, "f"):
                 categ_str: str = ser.cat.numRef.f
             elif hasattr(ser.cat, "strRef") and hasattr(ser.cat.strRef, "f"):
                 categ_str: str = ser.cat.strRef.f
+            else:
+                categ_str: str = ""
             series.append("{:},{:}".format(value_str, categ_str))
         series: str = ";".join(series)